Ethereum Sets October 6 Sepolia Test for Glamsterdam

Ethereum developers have set October 6, 2026, as the date for the Glamsterdam upgrade to fork on the Sepolia testnet. The date is listed as the next Glamsterdam milestone on Ethereum.org and was recorded during the September 17 All Core Developers Consensus call.

Developers also recorded October 27 as a tentative target for the Hoodi testnet. A mainnet activation date has not been confirmed.

The call also addressed a potential disruption to testing involving disposable block-builder identities. Developers said an operator could submit inflated bids, win blocks and then withhold the associated payloads on Sepolia.

The scenario concerns a free-to-use testing environment rather than mainnet user assets. Still, it could interfere with the testing process ahead of a future production-network rollout.

Sepolia is the next confirmed milestone

The October 6 Sepolia fork is the next confirmed step on the Glamsterdam roadmap. Hoodi remains tentatively scheduled for October 27, while developers have not set a mainnet date.

Testnet milestones allow developers to evaluate upgrade behavior before deciding on a mainnet schedule. The absence of a confirmed mainnet date means the current timeline should not be read as a final activation plan.

Glamsterdam-related technical changes have also prompted discussion of potential smart-contract effects, including gas repricing considerations.

Developers discuss builder-abuse risk

During the September 17 consensus call, developers described a scenario in which an attacker creates numerous builder identities on the testnet. Those builders could offer unusually high bids, win block-building opportunities and withhold payloads.

According to the discussion, the approach could disrupt Sepolia because the network is free to use. The concern is operational: withheld payloads could make the test environment less reliable for assessing the upgrade.

The reported scenario does not directly place mainnet user funds at risk. It is instead a risk to the quality and continuity of testnet testing, which developers will need to account for as Glamsterdam progresses.

• An operator could create disposable builder identities.
• Those identities could submit inflated bids to win blocks.
• Withholding payloads after winning could interfere with Sepolia testing.

What remains to be decided

The immediate schedule is clear for Sepolia, but the Hoodi date remains tentative and mainnet timing is still open. Further testnet results and developer review will shape the next decisions.

The warning illustrates why testnet work extends beyond validating code changes. Developers must also consider how testing infrastructure can behave under adversarial conditions before relying on its results for a mainnet upgrade.

Continue reading: Glamsterdam gas repricing considerations on BTCNews.

Continue reading: Ethereum protocol priorities on BTCNews.

Sources

• Ethereum.org: Glamsterdam
• EIPsInsight: AllCoreDevs – Consensus #187
• CoinDesk: Ethereum confirms Glamsterdam dates, but warns 'fake' builders could stall the chain

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